The present invention relates to a housing for a drive cylinder comprising a cylinder barrel which is made up of an inner tube and a coaxially arranged outer tube in direct radial, external contact with the inner tube, which it firmly encircles.
Such a housing has been proposed, see for example the German utility model G 8,204,795. In order to achieve low friction properties the inner tube in this case consists of synthetic resin material and in order to improve impact strength has a surrounding outer tube of metal. The selected tube combination furthermore renders possible a relatively small wall thickness, this leading in turn to a reduction in weight. However problems have occurred in connection with producing a permanent, high quality inner surface on the barrel, along which the piston slides during operation. It is difficult to ensure smooth running on such inner surface within tolerable limits. Furthermore wear of the synthetic resin tube is responsible for problems and in the course of time will lead to leaks through the contact zone between the piston and the cylinder bore. Finally there are very exacting requirements as regards the accuracy of manufacture of the metal tube, since the inserted synthetic resin tube makes close contact with the bore of the outer tube and practically assumes the form thereof. Therefore among the difficulties involved there is a difficulty with the attachment of sensors, functioning to detect the position of the piston, on the outer periphery of relatively thin metal tubes so that measures taken to permit such attachment have an unfavorable effect on the accuracy of the outline or cross section of the barrel.